Conventionally, a lock-unlock system for a vehicle has been known that includes an in-vehicle device installed on the vehicle and a mobile terminal that can be carried by the user, and executes locking or unlocking a door of the vehicle by wireless communication between the in-vehicle device and the mobile terminal (see, for example, Patent Document 1). Patent Document 1 discloses a remote unit having a transponder as an example of the mobile terminal, and a unit on the vehicle side as an example of the in-vehicle device.
According to the technology of Patent Document 1, in response to receiving an electromagnetic wave for activation that is transmitted from the unit on the vehicle side, the remote unit replies with an ID code of an RF signal (an identification code of the remote unit). On the other hand, if it has been determined that the battery of the remote unit is dead, the remote unit receives power supplied by electromagnetic induction induced by the electromagnetic wave for activation that has been transmitted from the unit on the vehicle side, and replies with an ID code for the transponder (an identification code of the remote unit). The unit on the vehicle side executes locking or unlocking the door of the vehicle, based on a result of verification of the ID code of the RF signal or the ID code for the transponder.
In this way, if a predetermined condition is satisfied, the system in Patent Document 1 automatically switches from control for verifying the identification code of the remote unit in a communication mode using the RF signal, to control for verifying the identification code of the remote unit in a communication mode using electromagnetic induction.